Pour lemon juice over the apple chunks so that they don't turn brown.
Add apples into the pot and pour all the water over the apples.
Bring to a boil, cover and cook apples until soft for about 30 minutes.
Remove from heat and strain the apples with a cheesecloth and collect the apple juice. Don' t press the apples too much because that can cloud the apple juice. We want the jelly to look clear.
Bring the apple juice back to the heat with the sugar (please see my notes below for amount).
It should start to cook, bring to a rolling boil and then decrease the heat a bit but make sure it still cooks.
Cook down the jelly until you have reached setting temperature with the thermometer. Also, check if the jelly has set by adding a drop of hot jelly on an ice cold spoon or plate which you kept previously in the freezer. Read my tips in the post further up!
Once the jelly is set get your sterilized clean jam jars and fill the jars until the rim with the jelly substance.
Add some alcohol into the lid to kill the remaining germs. Close the jar tight and turn it quickly upside down. This will create a vacuum and it will help the jelly remain good for a longer period of time.
After 24 hours, turn the jars back to normal and stick a label on them so that you know when you made them and what it is.
Use as much sugar as you have liquid after you have strained the apples and were left with the apple juice. That means for example if you have 800-milliliter apple juice after cooking, use and add 800 grams sugar to the apple juice. It has to be an equal amount, do not cut on the sugar or the jam won't set and it will turn bad within weeks. The sugar preserves the jelly! Very important. People usually just use 1 teaspoon of jelly on a toasted bread, that is how French are never overweight. Moderation is the key.